Prior work on patient samples and tumor cell lines has shown that overexpression and mutation of p53 and low expression of the apoptosis-blocking proteins Bcl-xL and Bcl-2 correlate with chemotherapy response and successful organ preservation using sequential chemoradiation. The next step is to prospectively evaluate these molecular markers in clinical trials for their predictive value for chemotherapy response, organ preservation, and survival in order to select patients properly and avoid unnecessary morbidity and therapeutic redundancy. These data will allow the rationale design of future treatment paradigms where patients are selected for optimum therapy based upon the molecular profile of the tumors. A comprehensive research program is proposed to investigate the role of the p53 tumor suppressor gene and the Bcl-2 family of genes in the chemo/radiosensitivity of advanced laryngeal and hypopharyngeal squamous cell carcinoma. The hypothesis to be tested is that a combination of p53 mutation status and expression of the Bcl-2 family of genes determines the mechanism of cell death and response to chemoradiation regimens. Concurrent with the clinical investigations, in vitro studies will be performed to directly assess the impact of manipulation of p53 and Bcl-2 status upon chemotherapy and radiation sensitivity. We plan to test our hypothesis by executing the following specific aims: (1) To prospectively determine if a combination of apoptosis gene markers (p53, Bcl-2, Bcl-xl) predict response to neoadjuvant chemotherapy, organ preservation and survival in patients with advanced laryngeal and hypopharyngeal cancer; and (2) To test the hypothesis that cisplatin and radiation resistance in tumor cells can be overcome by direct inhibition of apoptosis-blocking genes using gene transfection strategies and small molecule inhibitors of Bcl-2 and Bcl-xL in in vitro model systems. Furthermore, we will test the hypothesis that transfection of dominantnegative p53 mutations will enhance the sensitivity of HNSCC cell lines to radiation and chemoradiation.